1. Field of the Invention
The present invention relates to a plasma reactor, specifically, to a method and apparatus used in the manufacture of integrated circuits and other electronic devices. More particularly, the invention relates to modifying and uniformly distributing the gas concentration of a meta-stable or atomic species over a wafer in a downstream plasma reactor.
2. Description of Related Art
Plasma-based reactions have become increasingly important to the semiconductor industry, providing for precisely controlled thin-film depositions, thin film etching, and surface treatment such as cleaning. In a deposition process, thin films are applied to semiconductor wafers; whereas, an etching process is generally used in semiconductor manufacture to remove exposed portions of the deposited film for the purpose of patterning the film. One possible method for depositing films, such as a nitride film, is a remote plasma technique. In this method, a plasma is generated at a location which is separate from the wafer. Unlike non-remote plasma processes, downstream plasma processing allows for non-wet chemical processing while eliminating plasma-induced device damage. The plasma products are allowed to flow over the wafer. In this manner, the wafer is not subjected to ion or electron bombardment, or the high heat loads typical of in-situ plasma systems. The plasma source is also equally appropriate for etching and cleaning as it is for depositing.
Candidates for downstream processing are those reactions initiated by atomic species or molecular fragments that can be generated within an active (glowing) plasma. Downstream processing generates a chemical reaction between reactive gas effluents flowing from the plasma source and the materials on the wafer. Downstream reactions are driven by the concentration and flow speed of the reactant flux to the wafer surface, the reaction rate constant, and the removal of reaction products from the reaction site. One difficulty arises, however, when a non-excited gas is required to be injected into the chamber concurrently with an excited gas. Typically, two independent chamber input ports are needed to supply both gases. The introduction of gases from two separate ports complicates the distribution of the gas mixture over the wafer surface leading to film non-uniformity.
The remote plasma enhanced chemical vapor deposition (PECVD) process affords greater control over the thin-film chemistry than the conventional PECVD process by restricting plasma excitation to a subset of the process gases, and thereby reducing the number of possible reaction pathways. The physical arrangement of a remote PECVD chamber is designed to make the process flow sequential or serial, rather than parallel as in a conventional or direct PECVD processes. A description of a remote PECVD process can be found in J. A. Theil, et al., xe2x80x9cEFFECTS OF NH3 AND N2 SOURCE GASES AND PLASMA EXCITATION FREQUENCIES ON THE REACTION CHEMISTRY FOR Si3N4 THIN-FILM GROWTH BY REMOTE PLASMA-ENHANCED CHEMICAL-VAPOR DEPOSITIONxe2x80x9d, J. Vac. Sci. Technology, A 10(4), July/August 1992, pp. 719-727.
Typically, a remote PECVD deposition process consists of the following steps: a) RF excitation of a first gas or gas mixture; b) transport of the excited species out of the plasma region into a chamber; c) introduction of a second gas over the substrate surface; and d) a CVD reaction at a substrate supported within the chamber to generate a thin dielectric film. For example, if a thin film silicon nitride were desired, the first gas would contain nitrogen, and the second gas would include a silicon containing gas such as Silane, SiH4.
FIG. 1 is a schematic representation of a prior art remote PECVD chamber 10. Importantly, these remote PECVD chambers provide for RF coils 12 surrounding a tube 14, typically a PYREX(copyright) tube, to inductively excite a gas delivered at the top 16 of reactor 10. The excited gas is then transported into chamber 20 through input port 18. The gas disperses within chamber 20 and reacts with substrate 22 which is supported on pedestal 24. A similar PECVD chamber has been previously discussed by D. V. Tsu, et al., in xe2x80x9cLOCAL ATOMIC STRUCTURE IN THIN FILMS OF SILICON NITRIDE AND SILICON DIIMIDE PRODUCED BY REMOTE PLASMA-ENHANCED CHEMICAL-VAPOR DEPOSITION,xe2x80x9d Physical Review B, Volume 33, Number 10, May 15, 1996, p. 7070. In the Tsu invention, a second gas is delivered through a feed-through tube to a gas dispersal ring that is placed over the substrate. This second gas is typically delivered through a second input port, shown in FIG. 1 as covered by plate 19. Although the second gas delivery apparatus, i.e., gas dispersal ring, is not common to all prior art remote PECVD chambers, it nevertheless further contributes to gas concentration non-uniformity at the wafer surface. It also represents a current prior art method for introducing a second, unexcited gas into the chamber.
Process uniformity has been previously attempted by establishing the flow dynamics that help control a uniform species distribution across the reacting surface. An inherent disadvantage of a remote plasma system, however, is the lack of acceptable process uniformity of the gas distribution at the wafer or substrate level. Since the active gases created by the plasma are delivered to the process chamber and not created in it, the distribution of gases inside the chamber is very difficult to control due to unwanted reactions on the chamber surfaces which consume the active gases. If the reactive gas flows in from the side of the reactor, with respect to the wafer, the concentration will be high in the center of the wafer and low at the edges.
In typical (non-remote) Chemical Vapor Deposition (CVD) or Plasma Enhanced Chemical Vapor Deposition (PECVD) reactors, a showerhead is used to make the gas distribution uniform over the wafer. This strategy is not suitable for downstream reactors because the active gasses would have to flow past the baffle and faceplate holes which make up the showerhead. The showerhead elements also have the effect of destroying the active species needed for remote processing.
In the case of an active atomic species being generated in the remote plasma, the showerhead elements promote recombination. In the case where the remote plasma generates a meta-stable species, the showerhead elements promote xe2x80x9cquenchingxe2x80x9d or deactivation of the species.
The distribution of gas during plasma processing can also be affected by the introduction of a second gas. Concurrent injection of two gases (or gas mixtures) is typically performed by introducing the second (unexcited) gas through a separate input port into the chamber. However, this second injection will alter the uniform distribution of the excited gas, requiring that at least two separate distribution normalization systems or processes be employed. An apparatus and method capable of concurrent injection through the same input port would allow for unique advantages in the distribution normalization of the gas mixture, and eliminate the need for a second input to the chamber.
Additionally, concurrently providing two independent gases to the chamber through the same plasma confinement tube, one gas of which is excited by the plasma source while the other is isolated from the RF inductive and infrared radiated energies, facilitates the simultaneous introduction of diverse gas mixtures within the process chamber. Also, one may introduce a single gas within the chamber causing it to have an excited component and a non-excited component.
A supersonic CVD gas jet source for deposition of thin films has been developed in U.S. Pat. No. 5,256,205, issued to J. Schmitt, et al., entitled xe2x80x9cMICROWAVE PLASMA ASSISTED SUPERSONIC GAS JET DEPOSITION OF THIN FILM MATERIALS.xe2x80x9d This source has been used to produce a high dielectric constant for thin film semiconductor applications, e.g., Si3N4. However, this source does not provide for simultaneous delivery of active and molecular (non-activated or dissociated) gas species.
Also, it is advantageous to have a source that is not dependent upon the supersonic flow of the material to be deposited on the semiconductor substrate. It is beneficial to have material transport and growth not made dependent only upon diffusion kinetics in high vacuum, e.g., 300 mTorr. Less process gas flow at lower chamber pressures will reduce chamber design and construction constraints.
Lastly, prior art sources of concurrent gas delivery systems are limited to an area at the wafer surface about 1 cm to 2 cm in diameter, restricted mainly by the Laval nozzle dimension, and require translation of the substrate in a complex motion in front of the nozzle in order to achieve deposition over an entire substrate of any dimension greater than approximately 1 cm.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide an apparatus and method for injecting gases and enhancing the uniformity of the active species in a remote downstream plasma reactor.
It is another object of the present invention to provide an apparatus and method for tailoring the gas concentration distribution of a remote PECVD process for wafer-edge or wafer-center concentrations.
A further object of the invention is to provide an apparatus and method for varying the gas concentration distribution across a wafer in a remote PECVD process.
Another object of the invention is to provide a remote PECVD source that can deposit uniform thin films across the entire field of the substrate with no movement or translation of the substrate or source.
It is yet another object of the present invention to provide a remote PECVD process that minimizes the loss of reactive species.
A further object of the present invention is to provide an apparatus and method to introduce gases into the chamber concurrently, through the plasma tube, having one gas excited by the plasma tube energies and the other remaining unexcited and shielded from the plasma tube energies.
Still other advantages of the invention will in part be obvious and will in part be apparent from the specification.
The above and other advantages, which will be apparent to one of skill in the art, are achieved in the present invention which is directed to, in a first aspect, a method for modifying gas flow distribution during chemical vapor deposition on a substrate within a remote plasma reactor chamber, comprising the steps of: a) establishing a remote plasma region by exciting a gas mixture with RF energy in a location removed from the chamber; b) injecting the gas mixture into the plasma region; c) transporting the excited gas mixture from the remote plasma region through an input port into the chamber; and, d) distributing the excited gas mixture over the substrate to a predetermined profile.
The method further includes causing the excited gas mixture to diffuse from the remote plasma region inward toward the chamber. The method also includes, in step (d), adjusting a contoured plate by changing the distance from the plate to the substrate to establish the predetermined profile. The predetermined profile comprises a wafer-edge concentrated distribution or a wafer-center concentrated distribution.
In a second aspect, the invention is directed to a method for modifying gas flow distribution during deposition on a substrate within a remote plasma reactor chamber, comprising the steps of: a) establishing a remote plasma region by exciting a gas mixture with RF energy in a location removed from the chamber; b) transporting the excited gas mixture from the remote plasma region through an input port in the chamber; c) redistributing the transported gas mixture within the chamber by providing a contoured plate of predetermined diameter between the input port and the substrate, the plate having a distance to the substrate; and, d) adjusting the distance to modify the gas flow distribution to the substrate.
In a third aspect, the invention is directed to a remote plasma reactor for processing a workpiece, comprising: a chamber enclosure having an input port; a remote plasma source connected to the input port and adapted to provide a means for gas transport from the source to the chamber through the input port; an inductive coil surrounding a portion of the remote plasma source capable of inductively coupling RF energy from an RF power supply; a pedestal within the chamber defining thereon a workstation to support the workpiece; and, a profiler plate within the chamber and mounted between the input port and the workpiece, the profiler plate being contoured and having a predetermined diameter and placed a predetermined distance from the workpiece.
The profiler plate is symmetric about a center axis, having a narrow top portion and a wide bottom portion, the narrow top portion mounted closest to the input port and the axis centered with the input port.
In a fourth aspect, the invention is directed to an apparatus for modifying the gas distribution within a remote plasma enhanced chemical vapor deposition reactor having a chamber with an input port, the apparatus comprising: an axial symmetrical plate having a narrow top end and a bottom end wider than the top end, and centered with respect to the input port; and, an adjustable height securing clamp connecting the plate to the reactor adjacent to the input port.
In a fifth aspect, the present invention is directed to an apparatus for concurrently administering at least two gases into a plasma excitation region of a remote plasma enhanced chemical vapor deposition reactor, comprising: a chamber having at least one input port for the gas delivery and a pedestal for securing a semiconductor wafer; a coaxial injector tube attached to the chamber, including: an outer tube for confining a first gas for plasma excitation and defining the plasma excitation region; and, an inner tube within the outer tube, for delivery of a second gas through the plasma excitation region such that the second gas remains unexcited after traversing through the plasma region.
The inner tube passes axially and concentrically through the length of the outer tube and the tubes are comprised of a dielectric material. The inner tube further comprises: a metal gas tube; a dielectric inner sleeve external to and axially concentric with the metal gas tube; a Faraday shield external to and axially concentric with the dielectric inner sleeve; and, a dielectric outer sleeve external to and axially concentric with the Faraday shield. The Faraday shield may also include an infrared reflective coating.
The present invention is directed to, in a sixth aspect, an apparatus for administering gas into a plasma excitation region of a remote plasma enhanced chemical vapor deposition reactor, comprising: a chamber having at least one input port for the gas delivery and a pedestal for securing a semiconductor wafer; a coaxial injector tube having a top end and a bottom end, attached to the chamber at the bottom end, including: an outer tube confining a first gas for plasma excitation and defining the plasma excitation region; and, an inner tube within the outer tube, for delivery of a second gas through the plasma excitation region such that the second gas remains unexcited after traversing through the plasma excitation region; and, a contoured plate having a center hole, slideably attached to the coaxial injector tube through the center hole.
The present invention is directed to, in a seventh aspect, a method for injecting two gas mixtures into a remote plasma enhanced chemical vapor deposition reactor such that a first gas is excited by plasma energy while a second gas remains unexcited by the plasma energy, the method comprising: a) providing the remote plasma enhanced chemical vapor deposition reactor having a remote plasma source, a chamber, and one input port for gas ingress into the chamber; b) establishing a plasma region by applying RF energy to energize plasma in the remote plasma source; c) injecting the first and second gases into the plasma region to the chamber through the input port; d) exciting the first gas with the plasma energy; and, e) shielding the second gas from the plasma energy such that the second gas remains in a non-excited state as it traverses through the energized plasma region.
In an eighth aspect, the present invention is directed to a method for injecting two gas mixtures into a remote plasma enhanced chemical vapor deposition reactor such that a first gas is excited by plasma energy while a second gas remains unexcited by the plasma energy, and normalizing the distribution of the gases on a wafer surface, the method comprising: a) providing the remote plasma enhanced chemical vapor deposition reactor having a remote plasma source, a chamber, and one input port for gas ingress into the chamber; b) adjusting and securing a contoured plate of predetermined diameter below the input port and above the wafer surface; c) establishing a plasma region by applying RF energy to energize plasma in the re mote plasma source; d) injecting the first and second gases into the plasma region to the chamber through the input port and towards the plate; e) exciting the first gas with the plasma energy; and, f) shielding the second gas from the plasma energy such that the second gas remains in a non-excited state as it traverses through the plasma region.